Shape selective reactions with zeolite catalysts modified with iron and/or cobalt

ABSTRACT

A zeolite catalyst composition suitable for para-selective conversion of substituted aromatic compounds, e.g. conversion of aromatic compounds to dialkylbenzene compounds rich in the 1,4-dialkylbenzene isomer. Such a composition comprises a zeolite catalyst component having a silica to alumina mole ratio of at least 12 and a constraint index of about 1 to 12, and a minor amount, e.g., at least 0.25 weight percent of the elements iron and/or cobalt and optionally the element phosphorus, said elements being present in the form of their oxides.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a division of the copending application ofChin-Chiun Chu, said copending application having Ser. No. 318,238,filed Nov. 4, 1981, now U.S. Pat. No. 4,380,685, which in turn is acontinuation-in-part of the abandoned application of Chin-Chiun Chu,said abandoned application having Ser. No. 150,868, filed May 19, 1980.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention disclosed herein relates to novel zeolite catalystcompositions useful for the shape selective conversion of aromaticcompounds to yield a product mixture in which the 1,4-dialkylbenzeneisomer content is substantially in excess of its normal equilibriumconcentration.

2. Description of the Prior Art

The disproportionation of aromatic hydrocarbons in the presence ofzeolite catalysts has been described by Grandio et al. in the OIL ANDGAS JOURNAL, Vol. 69, Number 48(1971).

U.S. Pat. Nos. 3,126,422; 3,413,374; 3,598,878; 3,598,879 and 3,607,961show vapor-phase disproportionation of toluene over various catalysts.

In these prior art processes, the dimethylbenzene product produced hasthe equilibrium composition of approximately 24 percent of 1,4-, 54percent of 1,3- and 22 percent of 1,2-isomer. Of the dimethylbenzeneisomers, 1,3-dimethylbenzene is normally the least desired product, with1,2- and 1,4-dimethylbenzene being the more useful products.1,4-Dimethylbenzene is of particular value, being useful in themanufacture of terephthalic acid which is an intermediate in themanufacture of synthetic fibers such as "Dacron". Mixtures ofdimethylbenzene isomers, either alone or in further admixture withethylbenzene, have previously been separated by expensivesuperfractionation and multistage refrigeration steps. Such a process,as will be realized, involves high operation costs and has a limitedyield.

Various modified zeolite catalysts have been developed to alkylate ordisproportionate toluene with a greater or lesser degree of selectivityto 1,4-dimethylbenzene isomer. Hence, U.S. Pat. Nos. 3,972,832,4,034,053, 4,128,592 and 4,137,195 disclose particular zeolite catalystswhich have been treated with compounds of phosphorus and/or magnesium.Boron-containing zeolites are shown in U.S. Pat. No. 4,067,920 andantimony-containing zeolites in U.S. Pat. No. 3,979,472. Similarly, U.S.Pat. Nos. 3,965,208 and 4,117,026 disclose other modified zeolitesuseful for shape selective reactions.

While the above-noted prior art is considered of interest in connectionwith the subject matter of the present invention, the conversion processdescribed herein, utilizing a crystalline zeolite catalyst of specifiedcharacteristics which has undergone the particular treatment disclosed,has not, insofar as is known, been previously described.

SUMMARY OF THE INVENTION

In accordance with the present invention, there has now been discoverednovel iron and/or cobalt zeolite catalyst compositions useful forconversion of aromatic hydrocarbon compounds. An especially advantageouselement of the invention comprises the selective production of the1,4-isomer of dialkylated benzene compounds. Such a process involvescontacting an alkylated aromatic compound, either alone or in admixturewith a suitable alkylating agent such as methanol or ethylene, with aparticular type of iron and/or cobalt modified crystalline zeolitecatalysts under suitable conversion conditions to effectdisproportionation or transalkylation of alkylbenzene compounds oralkylation of aromatic compounds and to selectively produce the1,4-dialkylbenzene isomer in excess of its normal equilibriumconcentration, i.e., to produce a product mixture enriched in the1,4-dialkylbenzene isomer.

The iron and/or cobalt modified catalyst compositions of the presentinvention essentially comprise a crystalline zeolite component having asilica to alumina ratio of at least about 12 and a constraint indexwithin the approximate range of 1 to 12. Such zeolite based catalystcompositions can be modified by initial treatment with a compoundderived from the elements iron (Fe) and/or cobalt (Co) to yield acomposite containing a minor proportion of an oxide of one or bothelements. In addition to treatment of the catalyst with the iron and/orcobalt-containing compounds, the zeolite-based catalyst may also betreated with a phosphorus-containing compound to deposit a minorproportion of an oxide of phosphorus thereon in addition to the oxide ofthe metal.

An embodiment of the disclosed invention is a process for the alkylationof aromatic compounds, in the presence of the herein described modifiedzeolite catalysts, with selective production of the 1,4-dialkylbenzeneisomer in preference to the 1,2- and 1,3-isomers thereof. Especiallypreferred embodiments involve the selective production of1,4-dimethylbenzene from toluene and methanol and1-ethyl-4-methylbenzene from toluene and ethylene.

Another embodiment contemplates the selective disproportionation ortransalkylation of alkylbenzene and polyalkylbenzene compounds in thepresence of the disclosed catalysts, thereby yielding 1,4-disubstitutedbenzenes in excess of their normal equilibrium concentration. Forexample, under appropriate conditions of temperature and pressure,toluene will disproportionate in the presence of these catalysts toproduce a benzene and dimethylbenzene mixture enriched in the desirable1,4-isomer.

DESCRIPTION OF SPECIFIC EMBODIMENTS

The crystalline zeolites utilized in the catalyst compositions hereinare members of a particular class of zeolitic materials which exhibitunusual properties. Although these zeolites have unusually low aluminacontents, i.e. high silica to alumina mole ratios, they are very activeeven when the silica to alumina mole ratio exceeds 30. The activity issurprising since catalytic activity is generally attributed to frameworkaluminum atoms and/or cations associated with these aluminum atoms.These zeolites retain their crystallinity for long periods in spite ofthe presence of steam at high temperature which induces irreversiblecollapse of the framework of other zeolites, e.g. of the X and A type.Furthermore, carbonaceous deposits, when formed, may be removed byburning at higher than usual temperatures to restore activity. Thesezeolites, used as catalysts, generally have low coke-forming activityand therefore are conducive to long times on stream betweenregenerations by burning carbonaceous deposits with oxygen-containinggas such as air.

An important characteristic of the crystal structure of this particularclass of zeolites is that it provides a selective constrained access toand egress from the intracrystalline free space by virtue of having aneffective pore size intermediate between the small pore Linde A and thelarge pore Linde X, i.e. the pore windows of the structure are of abouta size such as would be provided by 10-membered rings of silicon atomsinterconnected by oxygen atoms. It is to be understood, of course, thatthese rings are those formed by the regular disposition of thetetrahedra making up the anionic framework of the crystalline zeolite,the oxygen atoms themselves being bonded to the silicon (or aluminum,etc.) atoms at the centers of the tetrahedra.

The silica to alumina mole ratio referred to may be determined byconventional analysis. This ratio is meant to represent, as closely aspossible, the ratio in the rigid anionic framework of the zeolitecrystal and to exclude aluminum in the binder or in cationic or otherform within the channels. Although zeolites with silica to alumina moleratios of at least 12 are useful, it is preferred in some instances touse zeolites having substantially higher silica/alumina ratios, e.g.,1600 and above. In addition, zeolites as otherwise characterized hereinbut which are substantially free of aluminum, that is having silica toalumina mole ratios of up to infinity, are found to be useful and evenpreferable in some instances. Such "high silica" or "highly siliceous"zeolites are intended to be included within this description. Alsoincluded within this definition are substantially pure silica analogs ofthe useful zeolites described herein, that is to say those zeoliteshaving no measurable amount of aluminum (silica to alumina mole ratio ofinfinity) but which otherwise embody the characteristics disclosed.

Such zeolites, after activation, acquire an intracrystalline sorptioncapacity for normal hexane which is greater than that for water, i.e.they exhibit "hydrophobic" properties. This hydrophobic character may beused to advantage in some applications.

Zeolites of the particular class metal herein have an effective poresize such as to freely sorb normal hexane. In addition, the structuremust provide constrained access to larger molecules. It is sometimespossible to judge from a known crystal structure whether suchconstrained access exists. For example, if the only pore windows in acrystal are formed by 8-membered rings of silicon and aluminum atoms,then access by molecules of larger cross-section than normal hexane isexcluded and the zeolite is not of the desired type. Windows of10-membered rings are preferred, although in some instances excessivepuckering of the rings or pore blockage may render these zeolitesineffective.

Although 12-membered rings in theory would not offer sufficientconstraint to produce advantageous conversions, it is noted that thepuckered 12-ring structure of TMA offretite does show some constrainedaccess. Other 12-ring structures may exist which may be operative forother reasons and, therefore, it is not the present intention toentirely judge the usefulness of a particular zeolite solely fromtheoretical structural considerations.

Rather than attempt to judge from crystal structure whether or not azeolite possessses the necessary constrained access to molecules oflarger cross-section than normal paraffins, a simple determination ofthe "Constraint Index" as herein defined may be made by passingcontinuously a mixture of an equal weight of normal hexane and3-methylpentane over a sample of zeolite at atmospheric pressureaccording to the following procedure. A sample of the zeolite, in theform of pellets or extrudate, is crushed to a particle size about thatof coarse sand and mounted in a glass tube. Prior to testing, thezeolite is treated with a stream of air at 540° C. for at least 15minutes. The zeolite is then flushed with helium and the temperature isadjusted between 290° C. and 510° C. to give an overall conversion ofbetween 10% and 60%. The mixture of hydrocarbons is passed at 1 liquidhourly space velocity (i.e., 1 volume of liquid hydrocarbon per volumeof zeolite per hour) over the zeolite with a helium dilution to give ahelium to (total) hydrocarbon mole ratio of 4:1. After 20 minutes onstream, a sample of the effluent is taken and analyzed, mostconveniently by gas chromatography, to determine the fraction remainingunchanged for each of the two hydrocarbons.

While the above experimental procedure will enable one to achieve thedesired overall conversion of 10 to 60% for most zeolite samples andrepresents preferred conditions, it may occasionally be necessary to usesomewhat more severe conditions for samples of very low activity, suchas those having an exceptionally high silica to alumina mole ratio. Inthose instances, a temperature of up to about 540° C. and a liquidhourly space velocity of less than one, such as 0.1 or less, can beemployed in order to achieve a minimum total conversion of about 10%.##EQU1##

The Constraint Index approximates the ratio of the cracking rateconstants for the two hydrocarbons. Zeolites suitable for the presentinvention are those having a Constraint Index of 1 to 12. ConstrainIndex (CI) values for some typical materials are:

    ______________________________________                                                          C.I.                                                        ______________________________________                                        ZSM-4               0.5                                                       ZSM-5               8.3                                                       ZSM-11              8.7                                                       ZSM-12              2                                                         ZSM-23              9.1                                                       ZSM-35              4.5                                                       ZSM-38              2                                                         ZSM-48              3.4                                                       TMA Offretite       3.7                                                       Clinoptilolite      3.4                                                       Beta                0.6                                                       H-Zeolon (mordenite)                                                                              0.4                                                       REY                 0.4                                                       Amorphous Silica-Alumina                                                                          0.6                                                       Erionite            38                                                        ______________________________________                                    

The above-described Constraint Index is an important and even criticaldefinition of those zeolites which are useful in the instant invention.The very nature of this parameter and the recited technique by which itis determined, however, admit of the possibility that a given zeolitecan be tested under somewhat different conditions and thereby exhibitdifferent Constraint Indices. Constraint Index seems to vary somewhatwith severity of operation (conversion) and the presence or absence ofbinders. Likewise, other variables such as crystal size of the zeolite,the presence of occluded contaminants, etc., may affect the constraintindex. Therefore, it will be appreciated that it may be possible to soselect test conditions as to establish more than one value in the rangeof 1 to 12 for the Constraint Index of a particular zeolite. Such azeolite exhibits the constrained access as herein defined and is to beregarded as having a Constraint Index in the range of 1 to 12. Alsocontemplated herein as having a Constraint Index in the range of 1 to 12and therefore within the scope of the defined class of highly siliceouszeolites are those zeolites which, when tested under two or more sets ofconditions within the above-specified ranges of temperature andconversion, produce a value of the Constraint Index slightly less than1, e.g. 0.9, or somewhat greater than 12, e.g. 14 or 15, with at leastone other value within the range of 1 to b 12. Thus, it should beunderstood that the Constraint Index value as used herein is aninclusive rather than an exclusive value. That is, a crystalline zeolitewhen identified by any combination of conditions within the testingdefinition set forth herein as having a Constraint Index in the range of1 to 12 is intended to be included in the instant zeolite definitionwhether or not the same identical zeolite, when tested under other ofthe defined conditions, may give a Constraint Index value outside of therange of 1 to 12.

The particular class of zeolites defined herein is exemplified by ZSM-5,ZSM-11, ZSM-12, ZSM-23, ZSM-35, ZSM-38, ZSM-48 and other similarmaterials.

ZSM-5 is described in greater detail in U.S. Pat. Nos. 3,702,886 and Re.29,948. The entire descriptions contained within those patents,particularly the X-ray diffraction pattern of therein disclosed ZSM-5,are incorporated herein by reference.

ZSM-11 is described in U.S. Pat. No. 3,709,979. That description, and inparticular the X-ray diffraction pattern of said ZSM-11, is incorporatedherein by reference.

ZSM-12 is described in U.S. Pat. No. 3,832,449. That description, and inparticular the X-ray diffraction pattern disclosed therein, isincorporated herein by reference.

ZSM-23 is described in U.S. Pat. No. 4,076,842. The entire contentthereof, particularly the specification of the X-ray diffraction patternof the disclosed zeolite, is incorporated herein by reference.

ZSM-35 is described in U.S. Pat. No. 4,016,245. The description of thatzeolite, and particularly the X-ray diffraction pattern thereof, isincorporated herein by reference.

ZSM-38 is more particularly described in U.S. Pat. No. 4,046,859. Thedescription of that zeolite, and particularly the specified X-raydiffraction pattern thereof, is incorporated herein by reference.

ZSM-48 can be identified, in terms of moles of anhydrous oxides per 100moles of silica, as follows:

    (0-15)RN:(0-1.5)M.sub.2/n O:(0.2)Al.sub.2 O.sub.3 :(100)SiO.sub.2

wherein:

M is at least one cation having a valence n; and

RN is a C₁ -C₂₀ organic compound having at least one amine functionalgroup of pK_(a) ≧7.

It is recognized that, particularly when the composition containstetrahedral, framework aluminum a fraction of the amine functionalgroups may be protonated. The doubly protonated form, in conventionalnotation, would be (RNH)₂ O and is equivalent in stoichiometry to 2RN+H₂O.

The characteristic X-ray diffraction pattern of the synthetic zeoliteZSM-48 has the following significant lines:

    ______________________________________                                        Characteristic Lines of ZSM-48                                                d (Angstroms)  Relative Intensity                                             ______________________________________                                        11.9           W-S                                                            10.2           W                                                              7.2            W                                                              5.9            W                                                              4.2            VS                                                             3.9            VS                                                             3.6            W                                                              2.85           W                                                              ______________________________________                                    

These values were determined by standard techniques. The radiation wasthe K-alpha doublet of copper, and a scintillation counter spectrometerwith a strip chart pen recorder was used. The peak heights, I, and thepositions as a function of 2 times theta, where theta is the Braggangle, were read from the spectrometer chart. From these, the relativeintensities, 100 I/I_(o), where I_(o) is the intensity of the strongestline or peak, and d (obs.), the interplanar spacing in angstroms,corresponding to the recorded lines, were calculated. In the foregoingtable the relative intensities are given in terms of the symbols W=weak,VS=very strong and W-S=weak-to-strong. Ion exchange of the sodium ionwith cations reveals substantially the same pattern with some minorshifts in interplanar spacing and variation in relative intensity. Otherminor variations can occur depending on the silicon to aluminum ratio ofthe particular sample, as well as if it has been subjected to thermaltreatment.

The ZSM-48 can be prepared from a reaction mixture containing a sourceof silica, water, RN, an alkali metal oxide (e.g. sodium) and optionallyalumina. The reaction mixture should have a composition, in terms ofmole ratios of oxides, falling within the following ranges:

    ______________________________________                                        REACTANTS      BROAD       PREFERRED                                          ______________________________________                                        Al.sub.2 O.sub.3 /SiO.sub.2 =                                                                0 to 0.02   0 to 0.01                                          Na/SiO.sub.2 = 0 to 2      0.1 to 1.0                                         RN/SiO.sub.2 = 0.01 to 2.0 0.05 to 1.0                                        OH.sup.- /SiO.sub.2 =                                                                        0 to 0.25   0. to 1.0                                          H.sub.2 O/SiO.sub.2 =                                                                        10 to 100   20 to 70                                           H.sup.+ (added)/SiO.sub.2 =                                                                  0 to 0.2    0 to 0.05                                          ______________________________________                                    

wherein RN is a C₁ -C₂₀ organic compound having amine functional groupof pK_(a) ≧7. The mixture is maintained at 80°-250° C. until crystals ofthe material are formed. H⁺ (added) is moles acid added in excess of themoles of hydroxide added. In calculating H⁺ (added) and OH values, theterm acid (H⁺) includes both hydronium ion, whether free or coordinated,and aluminum. Thus aluminum sulfate, for example, would be considered amixture of aluminum oxide, sulfuric acid, and water. An aminehydrochloride would be a mixture of amine and HCl. In preparing thehighly siliceous form of ZSM-48 no alumina is added. Thus, the onlyaluminum present occurs as an impurity in the reactants.

Preferably, crystallization is carried out under pressure in anautoclave or static bomb reactor, at 80° C. to 250° C. Thereafter, thecrystals are separated from the liquid and recovered. The compositioncan be prepared utilizing materials which supply the appropriate oxide.Such compositions include sodium silicate, silica hydrosol, silica gel,silicic acid, RN, sodium hydroxide, sodium chloride, aluminum sulfate,sodium aluminate, aluminum oxide, or aluminum itself. RN is a C₁ -C₂₀organic compound containing at least one amine functional group ofpK_(a) ≧7, as defined above, and includes such compounds as C₃ -C₁₈primary, secondary, and tertiary amines, cyclic amine (such aspiperdine, pyrrolidine and piperazine), and polyamines such as NH₂--C_(n) H_(2n) --NH₂ wherein m is 4-12.

In all of the foregoing zeolites, the original cations can besubsequently replaced, at least in part, by calcination and/or ionexchange with another cation. Thus, the original cations can beexchanged into a hydrogen or hydrogen ion precursor form or a form inwhich the original cations have been replaced by a metal of, forexample, Groups II through VIII of the Periodic Table. Thus, it iscontemplated to exchange the original cations with ammonium ions or withhydronium ions. Catalytically active forms of these would include, inparticular, hydrogen, rare earth metals, aluminum, manganese and othermetals of Groups II and VIII of Periodic Table.

It is to be understood that by incorporating by reference the foregoingpatents to describe examples of specific members of the particular classwith greater particularity, it is intended that identification of thetherein disclosed crystalline zeolites be resolved on the basis of theirrespective X-ray diffraction patterns. As discussed above, the presentinvention contemplates utilization of such catalysts wherein the moleratio of silica to alumina is essentially unbounded. The incorporationof the identified patents should therefore not be construed as limitingthe disclosed crystalline zeolites to those having the specificsilica-alumina mole ratios discussed therein, it now being known thatsuch zeolites may be substantially aluminum-free and yet, having thesame crystal structure as the disclosed materials, may be useful or evenpreferred in some applications. It is the crystal structure, asidentified by the X-ray diffraction "fingerprint", which establishes theidentity of the specific crystalline zeolite material.

The specific zeolites described, when prepared in the presence oforganic cations, are substantially catalytically inactive, possiblybecause the intracrystalline free space is occupied by organic cationsfrom the forming solution. They may be activated by heating in an inertatmosphere at 540° C. for one hour, for example, followed by baseexchange with ammonium salts followed by calcination at 540° C. in air.The presence of organic cations in the forming solution may not beabsolutely essential to the formation of this type zeolite; however, thepresence of these cations does appear to favor the formation of thisspecial class of zeolite. More generally, it is desirable to activatethis type catalyst by base exchange with ammonium salts followed bycalcination in air at about 540° C. for from about 15 minutes to about24 hours.

Natural zeolites may sometimes be converted to zeolite structures of theclass herein identified by various activation procedures and othertreatments such a base exchange, steaming, alumina extraction andcalcination, alone or in combinations. Natural minerals which may be sotreated include ferrierite, brewsterite, stilbite, dachiardite,epistilbite, heulandite, and clinoptilolite.

The preferred crystalline zeolites for utilization herein include ZSM-5,ZSM-11, ZSM-12, ZSM-23, ZSM-35, ZSM-38, and ZSM-48, with ZSM-5 beingparticularly preferred.

In a preferred aspect of this invention, the zeolites hereof areselected as those providing among other things a crystal frameworkdensity, in the dry hydrogen form, of not less than about 1.6 grams percubic centimeter. It has been found that zeolites which satisfy allthree of the discussed criteria are most desired for several reasons.When hydrocarbon products or by-products are catalytically formed, forexample, such zeolites tend to maximize the production of gasolineboiling range hydrocarbon products. Therefore, the preferred zeolitesuseful with respect to this invention are those having a ConstraintIndex as defined above of about 1 to about 12, a silica to alumina moleratio of at least about 12 and a dried crystal density of not less thanabout 1.6 grams per cubic centimeter. The dry density for knownstructures may be calculated from the number of silicon plus aluminumatoms per 1000 cubic Angstroms, as given, e.g., on Page 19 of thearticle ZEOLITE STRUCTURE by W. M. Meier. This paper, the entirecontents of which are incorporated herein by reference, is included inPROCEEDINGS OF THE CONFERENCE OF MOLECULAR SIEVES, (London, April 1967)published by the Society of Chemical Industry, London, 1968.

When the crystal structure is unknown, the crystal framework density maybe determined by classical pyknometer techniques. For example, it may bedetermined by immersing the dry hydrogen form of the zeolite in anorganic solvent which is not sorbed by the crystal. Or, the crystaldensity may be determined by mercury porosimetry, since mercury willfill the interstices between crystals but will not penetrate theintracrystalline free space.

It is possible that the unusual sustained activity and stability of thisspecial class of zeolites is associated with its high crystal anionicframework density of not less than about 1.6 grams per cubic centimeter.This high density must necessarily be associated with a relatively smallamount of free space within the crystal, which might be expected toresult in more stable structures. This free space, however, is importantas the locus of catalytic activity.

Crystal framework densities of some typical zeolites, including somewhich are not within the purview of this invention, are:

    ______________________________________                                                      Void      Framework                                                           Volume    Density                                               ______________________________________                                        Ferrierite      0.28 cc/cc  1.76 g/cc                                         Mordenite       .28         1.7                                               ZSM-5, -11      .29         1.79                                              ZSM-12          --          1.8                                               ZSM-23          --          2.0                                               Dachiardite     .32         1.72                                              L               .32         1.61                                              Clinoptilolite  .34         1.71                                              Laumontite      .34         1.77                                              ZSM-4 (Omega)   .38         1.65                                              Heulandite      .39         1.69                                              P               .41         1.57                                              Offretite       .40         1.55                                              Levynite        .40         1.54                                              Erionite        .35         1.51                                              Gmelinite       .44         1.46                                              Chabazite       .47         1.45                                              A               .5          1.3                                               Y               .48         1.27                                              ______________________________________                                    

When synthesized in the alkali metal form, the zeolite can beconveniently converted to the hydrogen form, generally by intermediateformation of the ammonium form as a result of ammonium ion exchange andcalcination of the ammonium form to yield the hydrogen form. In additionto the hydrogen form, other forms of the zeolite wherein the originalalkali metal has been reduced to less than about 1.5 percent by weightmay be used as precursors to the iron and/or cobalt modified zeolites ofthe present invention. Thus, the original alkali metal of the zeolitemay be replaced by ion exchange with other suitable metal cations ofGroups I through VIII of the Periodic Table, including, by way ofexample, nickel, copper, zinc, palladium, calcium or rare earth metals.As discussed more fully hereinafter, incorporation of metal by ionexchange can contribute to the modification of the zeolites herein withiron and/or cobalt.

In practicing a particular hydrocarbon conversion process, it may beuseful to incorporate the above-described crystalline zeolites with amatrix comprising another material resistant to the temperature andother conditions employed in the process in order to thereby form thecomplete catalyst composition. Such matrix material is useful as abinder and imparts greater resistance to the catalyst for the severetemperature, pressure and reactant feed stream velocity conditionsencountered, for example, in many hydrocarbon conversion processes.

Useful matrix materials include both synthetic and naturally occurringsubstances, as well as inorganic materials such as clay, silica and/ormetal oxides. The latter may be either naturally occurring or in theform of gelatinous precipitates or gels including mixtures of silica andmetal oxides. Naturally occurring clays which can be composited with thezeolite include those of the montmorillonite and kaolin families, whichfamilies include the sub-bentonites and the kaolins commonly known asDixie, McNamee-Georgia and Florida clays or others in which the mainmineral constituent is halloysite, kaolinite, dickite, nacrite oranauxite. Such clays can be used in the raw state as originally mined orinitially subjected to calcination, acid treatment or chemicalmodification.

In addition to the foregoing materials, the zeolites employed herein maybe composited with a porous matrix material, such as alumina,silica-alumina, silica-magnesia, silica-zirconia, silica-thoria,silica-beryllia, and silica-titania, as well as ternary compositions,such as silica-alumina-thoria, silica-alumina-zirconia,silica-alumina-magnesia and silica-magnesia-zirconia. The matrix may bein the form of a cogel. The relative proportions of zeolite componentand inorganic oxide gel matrix, on an anhydrous basis, may vary widelywith the zeolite content ranging from between about 1 to about 99percent by weight and more usually in the range of about 5 to about 80percent by weight of the dry composite.

The zeolite catalyst compositions described hereinafter are, inaccordance with the present invention, modified by incorporating thereona minor amount of the elements iron and/or cobalt in the form of an ironoxide and/or a cobalt oxide. Iron and/or cobalt, as well as otheroptional components described hereinafter, can generally be incorporatedinto the catalyst composition by contacting the zeolite-containingcomposition with a solution comprising one or more compounds of theelements to be incorporated. Incorporation can occur by the mechanismsof ion exchange, adsorption and/or impregnation, the latter twophenomena commonly being referred to as "stuffing" techniques. It shouldbe emphasized that, while ion exchange can be used as one method forincorporating the iron, cobalt and/or other elements onto the zeolitecompositions described herein, ion exchange alone will generally notprovide the iron, cobalt and/or other elements within the zeolitecomposition in the requisite amount or in the desired form. Combinationsof incorporation techniques may be employed, for example, byincorporating one element by ion exchange and another element bystuffing.

Solutions of compounds of iron or cobalt, as well as of other elementsto be incorporated, may be formulated from any suitable solvent which isinert with respect to the iron or cobalt compound and the zeolite.Non-limiting examples of some suitable solvents include water, aliphaticand aromatic hydrocarbons, alcohols, organic acids (such as acetic acid,formic acid, propionic acid, and so forth), and inorganic acids (such ashydrochloric acid, sulfuric acid and nitric acid). Other commonlyavailable solvents such as halogenated hydrocarbons, ketones, ethers,etc., may be useful to dissolve some metal compounds or complexes.Generally, the most useful solvent will be found to be water. However,the solvent of choice for any particular compound will, of course, bedetermined by the nature of that compound and for that reason theforegoing list should not be considered exhaustive of all of thesuitable possibilities.

Representaive iron-containing compounds which can be used forincorporating iron into the zeolite-based compositions herein includeiron acetate, iron bromide, iron carbonate, iron perchlorate, ironchloride, iron citrate, iron fluoride, iron formate, iron iodate, ironiodide, iron lactate, iron malate, iron nitrate, iron oxalate, ironoxide, iron sulfate, iron sulfite, iron sulfide, iron tartrate and ironthiosulfate. This listing is not to be taken as encompassing all of theutilizable iron-containing compounds. It is merely intended to beillustrative of some of the representative metal compounds which thosein the art will find useful in practicing the disclosed invention. Theknowledgeable reader will readily appreciate that there are numerousother known iron salts and complexes which would prove useful herein toprovide solutions contaning iron suitable for combination with thezeolite in the manner hereinafter described.

Examples of representative cobalt-containing compounds which can be usedfor incorporating cobalt into the zeolite-based compositions hereininclude cobalt acetate, cobalt bromate, cobalt bromide, cobalt chlorate,cobalt chloride, cobalt perchlorate, cobalt fluoride, cobalt iodate,cobalt iodide, cobalt periodate, cobalt benzoate, cobalt nitrate, cobaltoxylate, cobalt oxide, cobalt formate, cobalt carbonate, cobaltpalmitate, cobalt sulfate, cobalt sulfite, cobalt sulfide and cobalttartarate. As discussed above with respect to the illustrative listingof iron compounds, the foregoing is not to be considered as a exhaustivelist of the utilizable cobalt salts and complexes. There are numerouscobalt compounds which the foregoing will suggest to those skilled inthe art as being suitable for providing the cobalt-containing solutionsfor treatment of the zeolite as hereinafter described.

Reaction of the zeolite composite with the treating iron or cobaltcompound is effected by contacting the zeolite with such compound. Wherethe treating compound is a liquid, such compound can be, as noted, insolution in a solvent at the time contact with the zeolite is effected.Any solvent relatively inert with respect to the treating iron and/orcobalt compound and the zeolite may be employed. Suitable solventsinclude water and aliphatic, aromatic or alcoholic liquids. The treatingcompound may also be used without a solvent, i.e., may be used as a neatliquid. Where the treating compound is in the gaseous phase, it can beused by itself or in admixture with a gaseous diluent relatively inertto the treating compound and the zeolite (such as helium or nitrogen) orwith an organic solvent such as octane or toluene.

Heating of the iron or cobalt compound containing catalyst subsequent topreparation and prior to use is preferred, and such heating cangenerally be carried out in the presence of oxygen--for example, in air.Although heating may be carried out at a temperature of about 150° C. ormore, higher temperatures, e.g., up to about 500° C., are preferred.Heating is generally carried out for 1-5 hours but may be extended to 24hours or longer. While heating temperatures above about 500° C. may beemployed, they are generally not necessary. After heating in air atelevated temperatures, and without being limited by any theoreticalconsiderations, it is contemplated that the iron and/or cobalt isactually present in the zeolite in an oxidized state, such as Fe₂ O₃ orCoO.

The amount of modifying oxide, e.g, iron oxide or cobalt oxide,incorporated in the zeolite should be at least about 0.25 percent byweight, calculated as elemental iron or elemental cobalt. However, it ispreferred that the amount utilized be at least about 1.0 percent byweight, particularly when the zeolite is combined with a binder, e.g.,35 weight percent of alumina. The amount of modifying oxide can be ashigh as about 30 percent by weight or more calculated as elemental ironor elemental cobalt depending on the amount and type of binder present.Preferably, the amount of modifying oxide added to the zeolite will bebetween about 1.0 and about 20 percent by weight, calculated aselemental iron or elemental cobalt.

The amount of iron and/or cobalt incorporated with the zeolite byreaction with the modifying element or compound thereof will depend uponseveral factors. One of these is the reaction time, i.e., the time thatthe zeolite and the iron and/or cabalt-containing source are maintainedin contact with each other. With greater reaction times, all otherfactors being equal, a greater amount of metal is incorporated with thezeolite. Other factors upon which the amount of iron and/or cobaltincorporated with the zeolite is dependent include reaction temperature,concentration of the treating compound in the reaction mixture, thedegree to which the zeolite has been dried prior to reaction with themetal-containing compound, the conditions of drying of the zeolite afterreaction with the treating compound, and the amount and type of binderincorporated with the zeolite.

In some instances, it may be desirable to modify the crystallinezeolites by combining therewith oxides of both iron and cobalt. Whensuch modification technique is employed, the respective oxides may bedeposited on the zeolite either sequentially or from a solutioncontaining suitable compounds of both elements, the oxides of which areto be combined with the zeolite. The amounts of oxides present in suchinstance are in the same range as specified above for the individualoxides, with the overall added oxide content being between about 1.0 andabout 25 weight percent of the composite, calculated on the basis ofelemental iron and cobalt.

A further embodiment of this invention includes additional modificationof the above metal oxide--zeolite composites with phosphorus, wherebyfrom about 0.25 weight percent to about 30 weight percent of an oxide ofphosphorus, calculated as elemental phosphorus, is combined with thezeolite. The preferred amount of phosphorus oxide will be between about1 weight percent and about 25 weight percent, based on the weight of thetreated zeolite and calculated as elemental phosphorus. The phosphorustreatment of the zeolite catalyst will preferably be carried out beforethe previously described modification with one or more of the specifiedmetals. Reaction of the zeolite compound with the phosphorus-containingcompound is carried out essentially as described above with respect tothe metal-containing compounds and it is preferred that the total amountof oxides combined with the zeolite, i.e. the phosphorus oxides plus themetal oxides, fall within the approximate range of 2 percent to 40percent by weight, based on the weight of the treated zeolite andcalculated on the basis of elemental phosphorus and elemental ironand/or cobalt.

Representative phosphorus-containing compounds which may be used includederivatives of groups represented by PX₃, RPX₂, R₂ PX, R₃ P, X₃ PO,(XO)₃ PO, (XO)₃ P, R₃ P═O, R₃ P═S, RPO₂, RPS₂, RP(O)(OX)₂, RP(S)(SX)₂,R₂ P(O)OX, R₂ P(S)SX, RP(SX)₂, ROP(OX)₂, RSP(SX)₂, (RS)₂ PSP(SR)₂, and(RO)₂ POP(OR)₂, where R is an alkyl or aryl, such as a phenyl radicaland X is hydrogen, R, or halide. These compounds include primary, RPH₂,secondary, R₂ PH and tertiary, R₃ P, phosphines such as butyl phosphine;the tertiary phosphine oxides R₃ PO, such as tributylphosphine oxide,the tertiary phosphine sulfides, R₃ PS, the primary, RP(O)(OX)₂, andsecondary, R₂ P(O)OX, phosphonic acids such as benzene phosphonic acid;the corresponding sulfur derivatives such as RP(S)(SX)₂ and R₂ P(S)SX,the esters of the phosphonic acids such as diethyl phosphonate, (RO)₂P(O)H, dialkyl alkyl phosphorates, (RO)₂ P(O)R, and alkyldialkylphosphinates, (RO)P(O)R₂ ; phosphinous acids, R₂ POX, such asdiethylphosphinous acid, primary, (RO)P(OX)₂, secondary, (RO)₂ POX, andtertiary, (RO)₃ P, phosphites; and esters thereof such as the monopropylester, alkyl dialkylphosphinites, (RO)PR₂, and dialkyl alkylphosphinite,(RO)₂ PR esters. Corresponding sulfur derivatives may also be employedincluding (RS)₂ P(S)H, (RS)₂ P(S)R, (RS)P(S)R₂, R₂ PSX, (RS)P(SX)₂,(RS)₂ PSX, (RS)₃ P, (RS)PR₂ and (RS)₂ PR. Examples of phosphite estersinclude trimethylphosphite, triethylphosphite, diisopropylphosphite,butylphosphite; and pyrophosphites such as tetraethylpyrophosphite. Thealkyl groups in the mentioned compounds contain from one to four carbonatoms.

Other suitable phosphorus-containing compounds include the phosphorushalides such as phosphorus trichloride, bromide, and iodide, alkylphosphorodichloridites, (RO)PCl₂, dialkyl phosphorochloridites, (RO)₂PCl, dialkylphosphinochloridites, R₂ PCl, alkylalkylphosphonochloridates, (RO)(R)P(O)Cl, dialkyl phosphinochloridates,R₂ P(O)Cl and RP(O)Cl₂. Applicable corresponding sulfur derivativesinclude (RS)PCl₂, (RS)₂ PCl, (RS)(R)P(S)Cl and R₂ (S)Cl.

Preferred phosphorus-containing compounds include diphenyl phosphinechloride, trimethylphosphite and phosphorus trichloride, phosphoricacid, phenyl phosphine oxychloride, trimethylphosphate, diphenylphosphinous acid, diphenyl phosphinic acid, diethylchlorothiophosphate,methyl acid phosphate and other alcohol-P₂ O₅ reaction products.

Particularly preferred are ammonium phosphates, including ammoniumhydrogen phosphate, (NH₄)₂ HPO₄, and ammonium dihydrogen phosphate, NH₄H₂ PO₄.

Another optional modifying treatment entails steaming of the zeolite bycontact with an atmosphere containing from about 5 to about 100 percentsteam at a temperature of from about 250° to about 1000° C. for a periodof between about 15 minutes and about 100 hours and under pressuresranging from sub-atmospheric to several hundred atmospheres. Preferably,steam treatment is effected at a temperature of between about 400° C.and about 700° C. for a period of between about 1 and about 24 hours.

Another optional modifying treatment involves precoking of the catalystcomposite to deposit a coating of between about 2 and about 75, andpreferably between about 15 and about 75, weight percent of cokethereon. Precoking can be accomplished by contacting the catalyst with ahydrocarbon charge, e.g. toluene, under high severity conditions oralternatively at a reduced hydrogen to hydrocarbon concentration, i.e. 0to 1 mole ratio of hydrogen to hydrocarbon, for a sufficient time todeposit the desired amount of coke thereon.

It is also contemplated that a combination of steaming and precoking ofthe catalyst under the above conditions may be employed to suitablymodify the crystalline zeolite catalyst.

Alkylation of aromatic compounds in the presence of the above-describedcatalyst can be effected by contact of the aromatic with an alkylatingagent. A particularly preferred embodiment involves the alkylation oftoluene wherein the alkylating agents employed comprise methanol orother well known methylating agents or ethylene. The reaction is carriedout at a temperature of between about 250° C. and about 750° C.,preferably between about 300° C. and 650° C. At higher temperatures, thezeolites of high silica/alumina ratio are preferred. For example, ZSM-5having a SiO₂ /Al₂ O₃ ratio of 30 and upwards is exceptionally stable athigh temperatures. The reaction generally takes place at atmosphericpressure, but pressures within the approximate range of 10⁵ N/m² to 10⁷N/m² (1-100 atmospheres) may be employed.

Some non-limiting examples of suitable alkylating agents would includeolefins such as, for example, ethylene, propylene, butene, decene anddodecene, as well as formaldehyde, alkyl halides and alcohols, the alkylportion thereof having from 1 to 16 carbon atoms. Numerous otheraliphatic compounds having at least one reactive alkyl radical may beutilized as alkylating agents.

Aromatic compounds which may be selectively alkylated as describedherein would include any alkylatable aromatic hydrocarbon such as, forexample, benzene, ethylbenzene, toluene, dimethylbenzenes,diethylbenzenes, methylethylbenzenes, propylbenzene, isopropylbenzene,isopropylmethylbenzenes, or substantially any mono- or di-substitutedbenzenes which are alkylatable in the 4-position of the aromatic ring.

The molar ratio of alkylating agent to aromatic compound is generallybetween about 0.05 and about 5. For instance, when methanol is employedas the methylating agent and toluene is the aromatic, a suitable molarratio of methanol to toluene has been found to be approximately 1-0.1moles of methanol per mole of toluene. Reaction is suitably accomplishedutilizing a feed weight hourly space velocity (WHSV) of between about 1and about 1000, and preferably between about 1 and about 200. Thereaction product, consisting predominantly of the 1,4-dialkyl isomer,e.g. 1,4-dimethylbenzene, 1-ethyl-4-methylbenzene, etc., or a mixture ofthe 1,4- and 1,2-isomers together with comparatively smaller amounts of1,3-dialkylbenzene isomer, may be separated by any suitable means. Suchmeans may include, for example, passing the reaction product streamthrough a water condenser and subsequently passing the organic phasethrough a column in which chromatographic separation of the aromaticisomers is accomplished.

When transalkylation is to be accomplished, transalkylating agents arealkyl or polyalkyl aromatic hydrocarbons wherein alkyl may be composedof from 2 to about 5 carbon atoms, such as, for example, toluene,xylene, trimethylbenzene, triethylbenzene, dimethylethylbenzene,ethylbenzene, diethylbenzene, ethyltoluene, and so forth.

Another aspect of this invention involves the selectivedisproportionation of alkylated aromatic compounds to producedialkylbenzenes wherein the yield of 1,4-dialkyl isomer is in excess ofthe normal equilibrium concentration. In this context, it should benoted that disproportionation is a special case of transalkylation inwhich the alkylatable hydrocarbon and the transalkylating agent are thesame compound, for example when toluene serves as the donor and acceptorof a transferred methyl group to produce benzene and xylene.

The transalkylation and disproportionation reactions are carried out bycontacting the reactants with the above described modified zeolitecatalyst as a temperature of between about 250° C. and 750° C. at apressure of between atmospheric (10⁵ N/m²) and about 100 atmospheres(10⁷ N/m²). The reactant feed WHSV will normally fall within the rangeof about 0.1 to about 50. Preferred alkylated aromatic compoundssuitable for utilization in this embodiment comprise toluene,ethylbenzene, propylbenzene or substantially any mono-substitutedalkylbenzene. These aromatic compounds are selectively converted to,respectively, 1,4-dimethylbenzene, 1,4-diethylbenzene,1,4-dipropylbenzene, or other 1,4-dialkylbenzene, as appropriate, withbenzene being a primary side product in each instance. The product isrecovered from the reactor effluent by conventional means, such asdistillation to remove the desired products of benzene anddialkylbenzene, and any unreacted aromatic component is recycled forfurther reaction.

The hydrocarbon conversion processes described herein may be carried outas a batch type, semi-continuous or continuous operation utilizing afixed or moving bed catalyst system. The catalyst after use in a movingbed reactor is conducted to a regeneration zone wherein coke is burnedfrom the catalyst in an oxygen-containing atmosphere, e.g. air, at anelevated temperature, after which the regenerated catalyst is recycledto the conversion zone for further contact with the charge stock. In afixed bed reactor, regeneration is carried out in a conventional mannerwhere an inert gas containing a small amount of oxygen (0.5-2%) is usedto turn the coke in a controlled manner so as to limit the temperatureto a maximum of around 500°-550° C.

The following examples will serve to illustrate certain specificembodiments of the hereindisclosed invention. These examples should not,however, be construed as limiting the scope of the novel invention asthere are many variations which may be made thereon without departingfrom the spirit of the disclosed invention, as those of skill in the artwill recognize.

EXAMPLE 1A [Alkylation reaction with unmodified ZSM-5]

Five grams of HZSM-5 (SiO₂ /Al₂ O₃ mole ratio=70; 65% on alumina binder)were placed in a quartz flow reactor and heated to temperature. A feedstream of toluene and methanol, at a molar ratio of 4 to 1, was passedover the heated zeolite at a weight hourly space velocity (WHSV) of 10.The results obtained at various temperatures are shown below.

    ______________________________________                                        Temperature Percent toluene                                                                           Percent para-isomer                                   °C.  conversion  in xylenes                                            ______________________________________                                        350         47.2        24.8                                                  400         58.0        24.4                                                  450         68.0        24.3                                                  500         87.6        24.2                                                  ______________________________________                                    

EXAMPLE 1B

In a similar manner, toluene was alkylated with ethylene by passingtoluene and ethylene, at WHSV of 7.0 and 0.5, respectively, over theheated ZSM-5. The results at various temperatures are shown below.

    ______________________________________                                                                Isomer ratios of                                      Temperature Percent toluene                                                                           ethyltoluene                                          °C.  conversion  p        m    o                                       ______________________________________                                        400         76.4        29.9     58.5 11.6                                    425         76.4        29.9     57.5 12.7                                    450         79.0        29.6     57.1 13.4                                    ______________________________________                                    

EXAMPLE 2 [Disproportionation reaction with unmodified ZSM-5]

Toluene was passed over 6 grams of the unmodified HZSM-5 zeolite ofExample 1 at temperatures ranging between 450° C. and 600° C. Thetoluene feed WHSV was maintained at 3.5-3.6. The results are summarizedbelow.

    __________________________________________________________________________    Temperature                                                                              Toluene Conversion                                                                      % Selectivity, wt                                                                       % para in                                      °C.                                                                           WHSV                                                                              Mole %    Benzene                                                                            Xylenes                                                                            xylene products                                __________________________________________________________________________    450    3.6  7.4      43.5 55.5 24.7                                           500    3.5 20.5      44.6 53.8 24.5                                           550    3.5 38.8      48.0 48.8 24.2                                           600    3.5 49.2      54.4 41.7 24.1                                           __________________________________________________________________________

EXAMPLE 3 [Preparation of Co-modified zeolite]

To a solution of 6.0 grams cobalt acetate in 15 ml of water at 80° C.were added 3.0 grams of HZSM-5 having SiO₂ /Al₂ O₃ =70. The mixture wasmaintained at 80° C.-90° C. for 2 hours. After filtration and drying atabout 90° C. for 2 hours, the residue was calcined at 500° C. for 2 morehours to give 3.15 g of Co-ZSM-5. The content of cobalt was found to be9.06% by weight.

EXAMPLE 4A [Alkylation reaction with Co-modified zeolite]

Alkylation of toluene with methanol was carried out by passing atoluene/methanol mixture (molar ratio of 4/1) over 1.1 g of the Co-ZSM-5catalyst of Example 3. The feed WHSV was 10 hour⁻¹ and the temperaturewas 400° C. Toluene conversion was 40.6% and selectivity to p-xylene inxylenes was 37.4%. This represents a very respectable increase inselectivity of more than 50% over that achieved by the unmodified ZSM-5(Example 1A).

EXAMPLE 4B

In a similar manner, ethylation of toluene was carried out by passingtoluene (at WHSV=7) and ethylene (at WHSV=0.5) over 1.1 g of theCo-ZSM-5 catalyst of Example 3 at 400° C. Conversion of toluene was51.8% and selectivity to p-ethyltoluene in ethyltoluenes was 53.6%.Under the same conditions of reaction the unmodified ZSM-5 (Example 1B)resulted in only a 29.9% selectivity to the para-isomer.

EXAMPLE 5 [Disproportionation reaction with Co-modified zeolite]

Disproportionation of toluene was carried out by passing a stream oftoluene over 1.1 g of the Co-ZSM-5 catalyst of Example 3 at WHSV=3.5 and500° C. Toluene conversion was 20.5% and selectivity to p-xylene inxylene was 26.0%.

EXAMPLE 6 [Preparation of P-modified zeolite]

Two hundred grams of the ammonium form of ZSM-5 (65% on alumina binder)were added to a solution of 80 g of diammonium hydrogen phosphate in 300ml of water. The mixture was allowed to stand at 90° C. for 2 hours,then the zeolite was removed by filtration, dried and calcianed for 2hours at 500° C. The P-ZSM-5 recovered contained 3.43 wt. % phosphorus.

EXAMPLE 7A [Alkylation reaction with P-modified zeolite]

Alkylation of toluene with methanol was carried out by passing atoluene/methanol mixture in a molar ratio of 4/1 through 5.0 g of theP-ZSM-5 zeolite of Example 6 while heating at the desired temperature:The feed WHSV was 10. The results obtained at the various temperaturesare shown below.

    ______________________________________                                        Temperature Percent Toluene                                                                           Percent para-isomer                                   °C.  Conversion  in Xylenes                                            ______________________________________                                        400         43.6        66.6                                                  450         54.4        57.7                                                  500         70.4        53.7                                                  550         85.2        52.0                                                  600         85.2        58.0                                                  ______________________________________                                    

EXAMPLE 7B

In a similar manner, alkylation of toluene with ethylene was carried outby passing toluene and ethylene, at a weight hourly space velocity of7.0 and 0.5, respectively, over the P-ZSM-5 at 400° C. Conversion oftoluene was 74.8% and selectivity to p-ethyltoluene was 55.5%.

EXAMPLE 8 [Disproportionation reaction with P-modified zeolite]

Disproportionation of toluene was carried out by passing toluene over5.0 g of the P-ZSM-5 zeolite of Example 6 at a weight hourly spacevelocity of 3.5 and temperatures of between 475° C. and 550° C. Theconditions and results are shown below.

    ______________________________________                                        Temperature                                                                            Toluene     % Selectivity, mole                                                                         % Para in                                  °C.                                                                             Conversion %                                                                              Benzene  Xylene Xylenes                                  ______________________________________                                        475      14.9        52.8     47.6   39.1                                     500      27.1        53.3     45.4   35.1                                     525      37.4        56.1     42.2   32.1                                     550      44.0        60.4     37.3   30.1                                     ______________________________________                                    

EXAMPLE 9 [Preparation of Fe-P-modified zeolite]

To a solution of 8.0 g of ferric nitrate in 10 ml water at 80° C. wereadded 6.0 g of the P-ZSM-5 of Example 6. The mixture was maintained at80° C.-90° C. for 2 hours, and then the zeolite was recovered byfiltration and dried at about 90° C. The residue was calcined at 500° C.for 2 hours to give 6.1 g of Fe-P-ZSM-5. Analysis showed the content ofiron to be 9.55% and that of phosphorus to be 1.55%.

EXAMPLE 10A [Alkylation reaction with Fe-P-modified zeolite]

Alkylation of toluene with methanol was carried out by passing atoluene/methanol mixture (molar ratio of 4/1) over 1.1 g of theFe-P-ZSM-5 catalyst of Example 9 at a feed WHSV of 10 hr⁻¹ and atemperature of 400° C. Toluene conversion was 43.2% and selectivity top-xylene in xylenes was 70.2%. Under the same conditions the P-ZSM-5resulted in a selectivity of only 66.6% (Example 7A).

EXAMPLE 10B

In a similar manner, ethylation of toluene was carried out by passingtoluene (at WHSV=7) and ethylene (at WHSV=0.5) over 1.1 g of theFe-P-ZSM-5 catalyst of Example 9 at 400° C. Conversion of toluene was83.2% and selectivity to p-ethyltoluene in ethyltoluenes was 73.4%. Thesame catalyst before modification with iron resulted in only 55.5%para-selectivity under the same conditions of reaction (Example 7B).

EXAMPLE 11 [Preparation of Co-P-modified Zeolite]

To a solution of 6.0 g of cobalt acetate in 15 ml of water at 80° C.were added 6.0 g of the P-ZSM-5 of Example 6. The mixture was maintainedat about 80° C.-90° C. for 2.5 hours. After filtration and drying atabout 90° C., the zeolite was calcined at 500° C. for an additional 2hours to give 6.58 g of Co-P-ZSM-5. Analysis indicated the content ofcobalt to be 10.6% and that of phosphorus to be 3.27%.

EXAMPLE 12A [Alkylation reaction with Co-P-modified zeolite

Alkylation of toluene with methanol was carried out by passing atoluene/methanol mixture (molar ratio of 4/1) over 5.0 g of theCo-P-ZSM-5 catalyst of Example 11 at a feed WHSV of 10 hr⁻¹ and atemperature of 400° C. Toluene conversion was 41.2% and selectivity top-xylene in xylenes was 88.0%. As can be seen from comparative Example7A, the same reaction utilizing the ZSM 5 which had been modified withphosphorus (but not with cobalt) resulted in a selectivity to thepara-isomer of only 66.6%.

EXAMPLE 12B

Ethylation of toluene was carried out by passing toluene (at WHSV=7) andethylene (at WHSV=0.5) over 5.0 g of Co-P-ZSM-5 catalyst of Example 11at 400° C. Conversion of toluene was 66.0% and selectivity top-ethyltoluene in ethyltoluenes was 91.2%. The P-ZSM-5 zeolite which hadnot been modified with cobalt resulted in only 55.5% para-selectivity(Example 7B).

EXAMPLE 13 [Disproportionation reaction with Co-P-modified zeolite]

Disproportionation of toluene was carried out by passing a toluene feedstream over 5.0 g of Co-P-ZSM-5 catalyst of Example 11 at WHSV=3.5 and500° C. Toluene conversion was 8.8% and selectivity to p-xylene inxylene was 60.1%. By contrast, the P-ZSM-5 (no cobalt) resulted inpara-selectivity of 35.1% under the same conditions of reaction (Example8).

EXAMPLE 14 [Alkylation reaction with unmodified ZSM-11]

A one gram portion of HZSM-11 zeolite (SiO₂ /Al₂ O₃ =70) was placed in aquartz flow reactor and maintained at 400° C.-450° C. A feed stream oftoluene and ethylene was passed over the heated catalyst at feed WHSV of7.5 hr⁻¹ and 0.55 hr⁻¹, respectively, and the reactor effluent analyzed.The results are summarized below.

    ______________________________________                                        Temperature Percent Toluene                                                                           % Para-isomer in                                      °C.  Conversion  Ethyltoluene                                          ______________________________________                                        400         80.2        27.3                                                  450         81.9        27.2                                                  ______________________________________                                    

EXAMPLE 15 [Disproportionation rection with unmodified ZSM-11]

A 1.0 g portion of unmodified HZSM-11 zeolite (silica to alumina moleratio=70) was placed in a quartz flow reactor and heated to temperature.Toluene was passed over the zeolite at WHSV of 3.8 hr⁻¹ and varioustemperatures between 400° C. and 600° C. The results are summarizedbelow.

    ______________________________________                                        Tem-    Toluene                                                               perature                                                                              Conversion                                                                              % Selectivity, mole                                                                         % para in                                     °C.                                                                            Mole %    Benzene  Xylene Xylene Products                             ______________________________________                                        400      3.0      51.7     47.8   24.3                                        450      8.7      48.1     50.7   24.1                                        500     21.7      49.0     48.9   23.7                                        550     39.1      53.7     42.6   23.7                                        600     49.9      58.6     36.8   23.4                                        ______________________________________                                    

EXAMPLE 16 [Preparation of Co-modified ZSM-11]

To a solution of 6.0 g cobalt acetate in 15 ml water at 80° C. wereadded 1.5 g HZSM-11 (SiO₂ /Al₂ O₃ =70). The mixture was maintained at80° C.-90° C. for 2 hours. After filtration and drying at about 90° C.for 16 hours, the zeolite was calcined for 2 more hours at 500° C. togive 1.78 g of Co-ZSM-11. The content of cobalt was found to be 14.7%.

EXAMPLE 17 [Alkylation reaction with Co-modified ZSM-11]

Ethylation of toluene was carried out by passing toluene (at WHSV=7) andethylene (at WHSV=0.5) over 1.1 g of the Co-ZSM-11 catalyst of Example16 at 400° C. Conversion of toluene was 57.5% and selectivity top-ethyltoluene in ethyltoluenes was 33.8%.

EXAMPLE 18 [Disproportionation reaction with Co-modified ZSM-11]

Disproportionation of toluene was carried out by passing toluene over1.1 g of the Co-ZSM-11 catalyst of Example 16 at WHSV=3.5 and 450° C.Toluene conversion was 3.0% and selectivity to p-xylene in xylene was27.7%.

It is to be understood that the foregoing is intended to be merelyillustrative of certain specific embodiments of the disclosed invention.As those of skill in the art will readily appreciate, there are manyvariations which may be made on these specific embodiments withoutdeparting from the spirit of the invention described herein, and suchvariations are clearly encompassed within ambit of the following claims.

What is claimed is:
 1. A catalyst composition suitable forpara-selective conversion of substituted aromatic compounds, saidcomposition comprising a crystalline zeolite catalyst componentcharacterized by a silica to alumina mole ratio of at least 12 and aconstraint index within the approximate range of 1 to 12, saidcomposition further having incorporated thereon at least 0.25 weightpercent of a metal selected from iron, cobalt and combinations thereofand at least 0.25 weight percent of the element phosphorus, said metaland said phosphorus both being in the oxide form when combined with saidcatalyst composition.
 2. The composition of claim 1 wherein said metalcomprises between 1 and 20 weight percent of the zeolite catalystcomposition.
 3. The composition of claim 2 wherein said metal is iron.4. The composition of claim 2 wherein said metal is cobalt.
 5. Thecomposition of claim 2 wherein said composition comprises a zeoliteadmixed with a binder therefor.
 6. The composition of claim 3 whereinsaid zeolite is selected from the group consisting of ZSM-5, ZSM-11,ZSM-12, ZSM-23, ZSM-35, ZSM-38 and ZSM-48.
 7. The composition of claim 4wherein said zeolite is selected from the group consisting of ZSM-5,ZSM-11, ZSM-12, ZSM-23, ZSM-35, ZSM-38 and ZSM-48.
 8. The composition ofclaim 5 wherein said zeolite is selected from the group consisting ofZSM-5, ZSM-11, ZSM-12, ZSM-23, ZSM-35, ZSM-38 and ZSM-48.
 9. A catalystcomposition suitable for para-selective conversion of substitutedaromatic compounds, said composition comprising a crystalline zeolitecatalyst component which is zeolite ZSM-5 and said composition furtherhaving incorporated thereon at least 0.25 weight percent of a metalselected from iron, cobalt and combinations thereof and at least 0.25weight percent of the element phosphorus, said metal and said phosphorusboth being in the oxide form when combined with said catalystcomposition.
 10. A catalyst composition suitable for para-selectiveconversion of substituted aromatic compounds, said compositioncomprising a crystalline zeolite catayst component which is ZSM-11 andsaid composition further having incorporated thereon at least 0.25weight percent of a metal selected from iron, cobalt and combinationsthereof and at least 0.25 weight percent of the element phosphorus, saidmetal and said phosphorus both being in the oxide form when combinedwith said catalyst composition.